Manufacture of aluminium



(No Model.)

'G. M. HALL. MANUFACTURE OF ALUMINIUM.

No. 400,665. Patented Apr. 2, 1889.

@JKIQSLM UNITED STATES 2 PATENT j cnnnmcs M. HALL, on outrun-1n, euro MAN u FACTU RE or ALu MQIN'IUM. v

' SPECIFICATION forming part of Letters Patent No.'400,66 5, dated April 2, 1889.

- Application tiled August 17, 1888. Serial No. 282,954. (No specimen a.)

To all whom it may concern-.-

lc it known that I,-CHARLES M. HALL, a citizen of. the United States, residing at Oberlin-, in the county of Lorain and State of Ohio,

have invented or discovered certain new and useful Improvements in the Manufacture of Aluminium, of which improvements the following is a specification. V

J In applications filed by me July 9, 1886, and February 2, 1887, numbered 207,601 and 226,206, respectively,- I have described and claimed certain processes for the reduction'of aluminium, wherein I employ fluoride salts of aluminium or double fluorides of aluminium and electro-positive metalsas,-for example, sodium or potassium.-in a fused state todissolve alumina, and the alumina is subjected to electrolysis when in a state of solution in the fused salts, thereby reducing aluminium at the negative electrode, the oxygen going to the positive elect-rode.v The bat-h formed of the double fluoride of aluminium andan alkal inc metal, as described in the above application, becomes less efficient after being subjected to electrolytic action for som'e time. This change does not result from any removal of aluminium fluoride or of fluorine from the bath, as no fluorine is separated; but a black or dark substance is formed in the bath,apparent-1y from the alkaline constituent of the same, which interferes with a free electrolytic action and increases the electrical resistance; hence it has been found necessary when employing the salts named to change the bath after a continuous use of the same.

The object of the inven tion described herein is to provide a bath wherein the reduction of aluminium from its oxide may be carried on continuously without diminution and without increasing the electro-motive forceof the current.

The accompanying drawing, forming a part of this specification, is in sectional elevation a form of apparatus .applicable for carrying out my invention.

In carrying out my invention Iprefer to emp'loya double fluoride of aluminium and calcium having a composition represented by the formula (aAl F This composition is formed byonehumlred and six ty-n inc parts of aluminthere are a-large number of similar double.

fluoridesof the same metals which may be used and which closely resemble the one named, and answer almost, if not quite, as well .as a bath for dissolving the alumina. Thus the double salt of the formula Ca Al F has been successfully employed in the electrolytic reduction of aluminium. Whether the bath employed contains Vproportionatelyanore or seems to make little dilference.

.70 less aluminium fluoride within wide limits.

In the practice of my invention the fiuor-- the material. carbon when pure aluminium is desired, are

ides above mentioned are placed in the carbonlined crucible or vessel 1, arranged in-the furnace 2, and subjected to sufficient heat to fuse Electrodes 3 and 4, formed 'of' connected toa suitable electric generator, as l a dynamo-electricmachine. ,If an alloy is desired, the negative electrode 4 is formed of the metal with whichit is desired to alloy the -aluminium. Aluminai'ntheform of bauxite, anhydrous oxide of aluminium, or any other suitable form of alumina, preferably the pure anhydrous oxide A1,,O artificially prepared,

is then dissolved in the fused bath, and being subjected to the action of the electric current aluminium is reduced at the negative electrode, and, if said pole is formed of some heavy metal, forms an alloy with it, which drops 01? and sinks to the bottomof the bath. Oxygen goes to the positive electrode, and combining therewith when formed of carbon, forms carbonic-acid gas oncarbonic oxide, the carbon being gradually consumed. Alumina is added to -the -batl 1' from time to time as the process is continued. J The solution of alumina in the fused bath of the double fluoride aluminium and calcm m is apparently heavier than the metal aluminbarium resemble each other very closely and i-unnaud hence this metal, if-unalloyed, rises may be employed interchangeably in this proafter being reduced and floats on the surface cess-as, for example, the salts represented 55 of the bath, where it is liable to loss by oxiby .the formulas CaAhF BaAl F and 5 dationpn contact with the air or with the SrAhF,,, may be employed inthesame way and positive electrode, where it is subjected to a the salts of strontium and barium, as well as strong oxidizing action; hence when reducother double fluorides of strontiumand in'g'pure aluminium the crucible 1 is provided aluminium and barium and aluminium, may 60 with. a cover, 5, provided with openings for be used in the manner stated in regard tothe 1o insertion of the electric conductors and the double fluoride of calcium and aluminium. escape of gasfrom the crucible, and with a The salts of strontium and barium are heavier.

partition, 6, ofcarbon extending down into than the calcium salt, but more fusible, the r I the bath and from side to side of the crucibles salt of barium being the most fusible, andap 6 5 and separating the two electrodes. As the pear especially well adapted for the reduction r 5 aluminium is reduced at the negative elecof aluminium from alumina dissolvedin them trode alone, it will rise on the same side of into its alloys with heavy metals, especially the partition with saidelectrode, and. hence copper, the negative electrode in such case will be protected bythe cover. and partition being formed of copper. 1o from anyoxidizin'g influences, the carbonic- The double fluorides of aluminium and the :0 acid gas and carbonic oxide being formed on alkaline-earth metals, barium, calcium, and. the oppesite si e of the partition;- As the opstrontium resemble eachother and difierfr'om eration continues, the cover is'removed from the double fluorides of aluminium and the time to time and the aluminium removed alkaline metals, as potassium and sodium, in '15 from the surface of the. bath; .that they do not change in efliciency or action 25 When it is desired to form alloys of alumi on being-charged with alumina andsubjected nium with iron, copper, or other heavy metal, to electrolytic action for the reduction of the negative electrode is formed "of "iron, aluminium, asis the case with the double copper, or other metal with which the alloy fluorides of aluminiumand the alkaline met 8 isto be formed. The aluminium, as it is reals.; .30 duced at the negative .electrode, takes up a I claim'herein as my invention- 4 portion thereof, and it the electrode is-formed 1. As an improvement in the art of manuof heavy metal the alloythus formed sinks ,facturing aluminium, the herein-described to the'bottomof, the crucible. .=In forming method, which consists infusingacombina- 85.

alloys with heavy metals the cover and partion of the fluoride of aluminium and the 35 tition;may be. dispensed with, as the .bath fluoride of an alkaline-earth metal, adding will protect the alloy from any oxidizing inalumina to the bath so formed. and passing a fineness. current of electricity throughthe-fnsed mass, it may be stated that means may be used to substantially as described. 9 lower the specific gravity of the bath by the 2. As an improvement inthe art of manu-- 4o addition to it of other 'salts'lighter tha'nthe -faeturing aluminium, the herein-described double 'fiuorid'e of calcium and aluminium, so method, which consists in fusing a eombinathat thspure aluminium willsink in the com- ,tion of the. fluoride of aluminium and the binati6n and thusbe protected from oxidation. fluoride of calcium, adding alumina to "the 95 Thus by the addition to the bath above debath so formed, and then passing acurrent of 45 scribed of about two-thirds its weight of. the electricity through the fused mass, substan double fluoride, potassium and aluminium, tially as set forth. Q -(K Al,F which is. comparatively a .very In testimony whereof I have hereunto set light saltfis formed acomposition lighter than my hand.

aluminium,- which will therefore sink when CHARLES Mi HALL. 5 e u d d b sr 's y pr tected. \Vitnesses:

,The double fluoride of aluminium and the W. B. CoRwIN,

alkaliu' earth metals, calcium,strontinm, and DARWIN S. \VOLCOrr. 

